Social problems and disrupted relationships with close, attachment figures are difficulties that are risk factors and/or symptoms of many mental health disorders. Theorists and researchers are increasingly coming to common conclusions: humans are social creatures and when social relationships are disturbed, problems with emotion and self-control arise. Examining disturbance in social functioning and attachment relationships in adolescence, using the brain and behavior as markers of the nature of the disturbance, could facilitate better understanding of how social factors prompt mental health difficulties. Adolescence is particularly important developmental period because brain systems supporting social and emotional processing are rapidly developing at this time. There is, specifically, an urgent need to better understand these difficulties among adolescents with borderline personality disorder (BPD), a severe mental health disorder, characterized by a mix of problems in social and emotional domains. BPD is major public health issue, given its association with extreme misery and debilitation. And yet, the disorder is understudied, particularly within adolescents. The major aims of this project are to (1) examine the relationship between caregiver-attachment relationships and brain and behavioral signs of social functioning and affiliation with peers, (2) determine whether neural and behavioral signs of social dysfunction predict BPD symptoms, and (3) discern whether social functioning and affiliation with peers mediates the relationship between attachment and BPD. Attachment will be measured with an innovative approach to coding caregiver-adolescent conflict interactions. Social functioning will be assessed at 9-months using an fMRI-based Trust Task, which provides indices of trust and collaboration. Connectivity in brain networks, particularly the attachment/affiliation network, during instances of high trust and collaboration within this task will be examined in association with attachment disturbance and BPD symptoms at baseline and over 18-months. Dr. Beeney, the award candidate, is a clinical psychology PhD, seeking to transition to an independent research program focused on social and developmental neuroscience of interpersonal and emotional disturbance and BPD. The above project represents a first step towards this goal. Within the training period, he seeks to train in (1) developmental psychopathology, particularly in relation to adolescent brain development, (2) to learn to analyze the brain as a system of neural networks rather than discreet regions, and (3) learn a life span approach to attachment and train in adolescent development. Drs. Stephanie Stepp and Erika Forbes, both Associate Professors at University of Pittsburgh, will mentor Dr. Beeney. Dr. Stepp is an expert in adolescent development of BPD and Dr. Forbes is an expert in developmental neuroscience of affective disorders. University of Pittsburgh, Department of Psychiatry is a leading research institution, with extensive research support, world-class developmental and neuroimaging researchers, and state-of-the-art brain imaging facilities.